Lipoxins, a novel class of arachidonic acid metabolites from the lipoxygenase pathway, have been recently shown to be involved in acute as well as chronic inflammatory reactions; these reactions have been implicated in bone resorption, especially in diseases such as periodontitis and rheumatoid arthritis. It has been well established that arachidonic acid and prostaglandins (arachidonic acid metabolites produced from the cyclooxygenase pathway) have profound and important effects on bone tissue and bone cell physiology/pathophysiology. A few reports have indicated that leukotrienes (arachidonic acid metabolites derived from the lipoxygenase pathway) may also affect bone metabolism. However, there appears to be no information available about the possible role of lipoxins in bone physiology. Our hypothesis is that lipoxins are directly involved in the regulation of bone cell metabolism and that lipoxins can modulate the normal responses of bone cells to other agonists. The aim of the proposed study is to investigate the role of lipoxins in osteoblastic cell physiology. This study will: 1) Determine whether lipoxins can affect the metabolism of osteoblastic cells. the effects of lipoxins A4 and B4 on the metabolism of human osteoblastic osteosarcoma cell-lines Saos-2 and G292 will be tested. Effects on basal metabolism will be assessed by cell proliferation and protein synthesis. Alkaline phosphatase levels and the production of tissue plasminogen activator by the osteoblastic cells will also be followed. 2) Determine the signal transduction mechanisms by which osteoblastic cells respond to lipoxins. The effect of lipoxins A4 and B4 on classical signal transduction pathways (osteoblastic cell cAMP production, cytosolic calcium levels and phosphoinositide cycle) will be evaluated over time. Cyclic AMP studies will be performed using radioimmunoassay. Cytosolic calcium studies will be performed by fluorescence measurements on fura-2 loaded cells. Studies of phosphoinositide metabolism will be done by HPLC analysis of cellular inositol phosphates produced by 3H-inositol labelled cells. 3) Determine whether lipoxins can modulate the responses of osteoblastic cells to other osteotropic agents. The ability of lipoxins A4 and B4 to modulate the well characterized cAMP, phosphoinositide and cytosolic calcium responses of the Saos-2 and G292 cells to systemic (parathyroid hormone) and local (prostaglandin E2, thrombin, bradykinin) osteotropic agents will be evaluated. Knowledge of the effects that inflammatory agents, such as the lipoxins, may have on bone cells could provide a clearer understanding of the pathophysiology of periodontal bone loss. This understanding could lead to the development of rational and more effective pharmacological treatment modalities for periodontal disease as well as other disease states associated with inflammation-induced bone resorption.